As the need for electricity continues to grow, the need for higher capacity transmission and distribution lines grows as well. The amount of power a transmission line can deliver is dependent on the current-carrying capacity (ampacity) of the line. The ampacity of a line, however, is limited by the maximum safe operating temperature of the bare conductor that carries the current. Exceeding this temperature can result in damage to the conductor or to the transmission and distribution line accessories. The conductor temperature is determined by the cumulative effect of heating and cooling on the line. The conductor is heated by Ohmic losses and solar heat and cooled by conduction, convection and radiation. The amount of heat generated due to Ohmic losses depends on the current (I) and the electrical resistance (R) of the conductor and is determined by the relationship that Ohmic losses=I2R. Electrical resistance (R) itself is further dependent on temperature. Higher current and temperature leads to higher electrical resistance, which, in turn, leads to greater electrical losses in the conductor.
Several solutions have been proposed in the art to create higher capacity transmission and distribution lines. For example, overhead conductors coated with spectrally selective surface coatings are known. Such coatings can have a coefficient of heat emission (E) higher than 0.7 and coefficient of solar absorption (A) that is less than 0.3. Such coatings can be white in color to lower solar absorption.
Overhead cables having a black paint coating with an emissivity greater than 0.6 are also known. Such paints can be made of a plastic (e.g. polyurethane) and black color pigment.
Electric conductors coated with a polymeric layer whose emissivity coefficient is 0.7 or more and solar absorption coefficient is 0.3 or less are also known. Such polymeric layer can be produced from polyvinylidene fluoride (PVDF) and a white pigment additive.
However, many of these known coatings are white coatings that are not desirable due to glare and discoloration which can occur over time. Furthermore, polymeric coatings are also not desirable due to their questionable heat and wet aging characteristics.
Heat protective coatings are also generally known. However, such coatings are used to protect a substrate from heat external to the substrate, and do not cool the substrate by radiating heat to the external environment.
Therefore, there remains a need for a durable, inorganic, coating for overhead conductors that allow the conductors to operate at reduced temperatures.